Which Trees Absorb Carbon Best?

New global study reveals forests’ hidden carbon flaws — and how to fix them

In a warming world, maximising carbon drawdown demands choosing the right plants in the right places — not just planting more trees.

A groundbreaking analysis of 2,737 ecosystems worldwide has uncovered critical secrets about Earth’s carbon-absorbing “lungs.” It exposes why some forests squander carbon while others excel—with major implications for fighting climate change.

The Carbon Efficiency Gap

Carbon Use Efficiency (CUE) measures how well plants convert absorbed CO₂ into lasting biomass (wood, roots) versus losing it through respiration. The global study found:

• Forests are surprisingly wasteful: Average CUE = 0.41 (non-forests: 0.45).
• Deciduous trees dominate: Broadleaf forests (oak, maple) have 15% higher CUE than evergreens (pine, spruce).
• Crops are champions: Farmlands achieve CUE=0.50—the highest efficiency recorded.
• Savannas struggle: C4 grasslands scored just 0.32 due to high metabolic costs.

Climate’s Cruel Irony

As temperatures rise, plants’ carbon efficiency plummets — a dangerous climate feedback loop:

• CUE drops 5–7% per 1°C warming in temperate/tropical zones
• Rain and light reduce efficiency: More sun/water = more respiration waste
• Old forests decline: Efficiency peaks at 30–50 years, then falls

The study’s global map (Fig. 4a in the paper) reveals:

• CUE is lowest in the tropics (0.3–0.4) due to warmth, high rainfall, and dominance of evergreen forests.
• CUE peaks in cooler temperate/cropped zones (0.5–0.6), especially where deciduous trees or agriculture thrive.
• Latitudinal gradient is stark: Efficiency rises toward poles despite shorter growing seasons.

It means:

• Planting trees in the Amazon (low CUE) captures less long-term carbon per unit of photosynthesis than planting in degraded temperate grasslands (higher CUE).
• Reforestation priorities must account for baseline efficiency, not just growth speed or area.

You can access the global CUE map: here and the raw dataset here.

Four Rules for Smarter Carbon Sinks

Based on the data, the authors prescribe urgent shifts in conservation/restoration:

1. Plant Deciduous Over Evergreens

• Prioritise oak, birch, beech in reforestation
• Their lean tissue (lower leaf mass) reduces respiratory waste

1. Protect Young Forests

• Efficiency peaks at 30–50 years — old-growth preservation has diminishing returns
• Targeted thinning could maintain high CUE in mature stands

1. Value Non-Forest Ecosystems

• Grasslands/wetlands (CUE=0.46) often outperform forests
• Avoid converting these to low-efficiency tree plantations

1. Cool the Tropics

• Warm, bright conditions suppress CUE most severely
• Shading techniques or cloud-forest restoration could help

The Bigger Picture: Rethinking “Green” Solutions

This study challenges blanket approaches like mass tree-planting:

• Savanna afforestation could backfire: Natural grasslands (CUE=0.32) may lose efficiency if forested
• Crop potential unlocked: High farm efficiency (CUE=0.50) suggests bioengineering opportunities
• Carbon math matters: Switching evergreen to deciduous forests globally could capture +0.11 billion tons CO₂/year — equivalent to offsetting 10% of land-use emissions

The Path Forward

While forests remain vital, optimising carbon efficiency requires nuance:

• Revise climate models: Current DGVM (Dynamic general vegetation models) overestimate CUE by 15%
• Policy shifts: Initiatives like REDD+ should prioritise deciduous-native mixes
• Next-gen monitoring: Eddy covariance networks must expand to dry/remote zones

Source

Global variation in vegetation carbon use efficiency inferred from eddy covariance observations, Nature Ecology & Evolution, 2025-06-19